Recently, in a plate-making process of a printing plate for off-set printing, a CTP (computer to plate) system in which digital image data can be directly written in a light sensitive planographic printing plate material employing laser has been practically used. Provided are a type in which an aluminium base material is used as in the case of an existing PS plate, and a flexible type in which functional layers are formed on a film base material for printing plates, as a printing plate material used for the CTP system. A tendency toward a wide variety of printing products in small quantities has recently been observed in commercial printing, and printing plates with high quality at low price are highly demanded in the market. Known currently is a technique using a flexible type printing plate material and a printing plate developed for the market employing a plastic film sheet support which is easy to handle and carry (Refer to Patent Documents 1, 2, 3, and 4).
In the case of color printing employing a CTP printing plate material used for these plastic supports, a problem was that a printing plate with so-called high register accuracy caused “out of color registration” during printing, since four printing plates were employed in the color printing process. Another problem was that lowered printing image quality and insufficient printing durability appeared since a printing plate was deformed, and a convexoconcave structure appeared on the printing plate during printing.
(Patent Document 1) Japanese patent O.P.I. Publication No. 4-261539
(Patent Document 2) Japanese patent O.P.I. Publication No. 5-257287
(Patent Document 3) Japanese patent O.P.I. Publication No. 2000-258899
(Patent Document 4) Japanese patent O.P.I. Publication. No. 2002-79772